<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>盒子模型Title</title>
        <style>
            div{
                width: 200px;
                height: 200px;
                background-color: cyan;
                border: 10px solid mediumspringgreen;
                padding: 20px;
                margin: 50px;
                box-sizing: border-box;
            }
        </style>
    </head>
    <body>
        <div></div>
    </body>
</html>